1. Field of the Invention
The invention pertains to radar systems such as are used in marine navigation. More particularly, the invention relates to such radar systems employing collision avoidance capability.
2. Description of the Prior Art
Radar systems having collision avoidance capabilities, in limited use for several years, have recently become of greater importance due to government safety regulations in all major maritime nations. The systems of the known prior art were able to acquire and track targets and to indicate potential areas of collision. Unfortunately, these systems, although able to perform at longer ranges, were unable to track targets at close-in ranges, for example, under approximately three miles. One of the primary reasons why tracking was impossible was that these systems operated using the real-time video signal produced at the output of the radar receiver. At such short ranges, the times between the target signals appearing at the output of the receiver were typically too short for digital processors such as the anticollision apparatus to process. Moreover, because of the use of the real-time video signal, the display produced upon the radar cathode-ray tube was very dim at the short ranges.
Furthermore, in the known systems of the prior art, the equipment associated with the anticollision apparatus tended to be extremely complex to operate, require large amounts of electronic equipment including a separate display for the anticollision unit and requiring large amounts of space on the bridge of a ship.
It is desirable that the anticollision avoidance unit associated with a radar system provide many more functions other than simply tracking targets and warning of any impending collisions. For example, it may be desirable that map lines representing ship channels be drawn upon the cathode-ray tube screen for use in navigation. Or, it may be desired to draw lines on the screen of the cathode-ray tube designating areas in which target returns are to be ignored by the tracking circuitry. In the known systems of the prior art, it was not possible to readily modify the anticollision apparatus to be able to perform such additional functions.